Investigating the Behaviour of Acoustic Emission Waves near Cracks

142 Pages·2017·12.98 MB·English

Investigating the Behaviour
of Acoustic Emission Waves
near Cracks
Using the Finite Element Method
ing. N.L. van Rijn
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INVESTIGATING THE BEHAVIOUR OF
ACOUSTIC EMISSION WAVES NEAR CRACKS
USING THE FINITE ELEMENT METHOD
by
Nicolaas Leendert van Rijn
ing.
inpartialfulfillmentoftherequirementsforthedegreeof
MasterofScience
inOffshore&DredgingEngineering
StructuralAnalysisandDesign
attheDelftUniversityofTechnology,
tobedefendedpubliclyonTuesdayNovember14,2017at4:00PM.
Studentnumber: 4189329
Projectduration: December1,2016–November14,2017
Thesiscommittee: Prof.dr.ir.M.L.Kaminski, TUDelft,Supervisor,Chair
Ir.P.S.vanLieshout, TUDelft
Dr.Ir.P.T.L.M.vanWoerkom, TUDelft
Dr.B.Hu, AllseasEngineeringB.V.
Dr.Ir.N.S.Ermolaeva, AllseasEngineeringB.V.
Anelectronicversionofthisthesisisavailableathttp://repository.tudelft.nl/.

P A
REFACE AND CKNOWLEDGMENTS
ThisthesisisthefinalproductoftheresearchIconductedtoobtaintheMastersofSciencedegreeinOffshore
andDredgingEngineeringattheMechanicalMaritimeandMaterialsEngineeringfacultyofDelftUniversity
ofTechnology. TheworkhasbeencarriedoutattheInnovationsdepartmentofAllseasEngineeringB.V.in
Delft,incollaborationwiththe4D-Fatiguejointindustryproject.
MydeepestgratitudegoestoDr. BinHuandDr. NataliaErmolaevafortheopportunitytocarryoutthe
workdescribedinthisthesisatAllseasEngineeringB.V.Theirsupport,andthisproductiveenvironment,have
beenofgreatworth.IalsothankProf.dr.ir.M.L.KaminskiandIr.PaulavanLieshout,whohaveofferedme
thechancetocarryoutmyresearchinthefieldofacousticemission.Also,IwouldliketothankDr.ir.Paulvan
Woerkomforhisextensivefeedbackonmydraftreport.Furthermore,thanksgotothekindpeopleatVallen
SystemeGmbH.,whowereveryhospitableduringmystayattheircompany,andsharedtheirknowledgeon
acousticemissionwithme.ThanksgotoIr.MennovanderHorst,SylviavanKreveld,Ir.BartScheeren,Dr.ir.
TonRiemslagandIr.ThomasOpraus,whowereofgreathelpduringtheexperiments.Finally,Iwouldliketo
expressmygratitudetomyfamilyandfriends,whohavebeenaninvaluablesupportthroughouttheduration
ofmystudies.
ing.N.L.vanRijn
Delft,October2017
iii

A
BSTRACT
During fatigue crack growth of metallic structures, acoustic stress waves are introduced into the material.
Theseacousticemissionwavesaretheresultofthesuddenstressreleaseduringthenucleationofthecrack
surface. Using dedicated acoustic emission monitoring equipment, these waves can be recorded. When
multiple sensors are able to pick up the waves of a certain fatigue crack growth step, the location of this
crackcanbedeterminedbyusingthedifferencesintimeofarrivalofthesignalsatthesesensorlocations.
Thislocalizationisperformedbythemethodofmultilateration, whichisthesamemethodthatisusedto
calculatetheepicentreofearthquakes.
TU Delft and the 4D-Fatigue joint industry project will use acoustic emission to predict fatigue crack
depth,inordertodeterminethecrackgrowthrateinamulti-axialfatigueloadedtestspecimen.Thelocation
ofthefatiguecrackwillbeknown,sosensorscanbeappliedveryclosetoit. Thisuseofacousticemission
isunconventionalduetothefactthatmostappliancesfocusonamuchlargerscale,sincethisisoneofthe
advantagesofthismethod.Theaccuracygoalwhichissetduringthisprojectisalsofarexceedingtraditional
use,aimingatacrackdepthpredictionwithanerrorlessthan1mm. Littleliteratureonacousticemission
focusesonthiscloserange,inducingtheneedforadditionalresearch.
Thegoalofthisthesisistoperformfiniteelementsimulations,inordertodeterminethebehaviourof
acousticemissionwavesincloseproximityofthecrack. Thisknowledgeshouldbeusedtodeterminewhat
accuracyvaluesareachievable,andwhethertherearewaystoimproveonthisaccuracy.
ThefirststepinordertoachievethisgoalwasthesimulationofaHsu-Nielsensource,morecommonly
referredtoasapencilleadbreak. Thisisaverysimpletoperformacousticemissionsource,andwillserve
toestablishappropriatefiniteelementsimulationparameters. Thissimplefirststepisalsoconvenientto
establishtheeffecttheacousticemissionmonitoringequipmenthasontheobtainedsignals. Themultiple
filter steps which are performed by the hardware, and the frequency response of the sensor have a great
influence on the signal. Pencil lead breaks were performed on a steel plate of 5mm thickness, at several
distances of a sensor. Signals produced by the simulations were verified by the experimental signals in a
rangeof5mm–70mm,verifyingtheusedsimulationmethods.
Thenextstepwastosimulateactualfatiguegrowthinthesamesteelplateof5mmthickness.Experimen-
talsignalswereattemptedtobeacquiredduringfatiguetestsoftheplate.Thefatiguemachinethatwasused
however,turnedouttoproducehighamplitudenoise,makingitnotpossibletoobtainthedesiredsignals.
Sinceverificationofthesimulatedsignalswouldnotbepossible,severalsourcemodelswereinvestigatedin
ordertosimulatefatiguecrackgrowthacousticemission,comparingthelocalizationresultswitheachother.
Localizationusingconventionalmethodswereabletoachieveanaccuracyof0.6mm. Usinganewmethod
ofwavespeeddeterminationhowever,whichmakesuseofthesimulationresults,thelocalizationaccuracy
wasimprovedto0.4mm.
Thefinalstepwastoperformasimulationofaspecimenwhichisusedbythe4D-FatigueJIP.Thistubu-
larspecimencontainsflanges,whichreflectinboundwavesbacktothesensors,potentiallyinfluencingthe
localizationaccuracy. Thesimulationshowever,concludedthatthesereflectionsarriveaftertheinitialwave
haspassed. Theeffectonlocalizationwasfoundtobenegligible. Localizationusingconventionalmethods
wasnotfoundresultinreliabledata.Thisdecreaseinaccuracycomparedtotheaccuracyfoundinthe5mm
plate,isattributedtothelargerdifferencesintraveldistancethesignalshave,duetothe10mmthickbody
ofthetubularspecimen. Localizationusingthenewspeeddeterminationmethod,resultedinalocalization
accuracyofapproximately1mm.
Althoughlocalizationaccuracywasfoundtobesufficienttosatisfytheinitialgoalof1mm,itshouldbe
notedthatthelocalizationwasperformedusinganestimatednoiseamplitudevalue. Also,duringthesenu-
mericalsimulationsthesensorisexactlyknown,whichisnotthecaseduringexperiments,soadditionalloca-
tionerrorshouldbetakenintoaccount.Theworkinthisthesisdoeshoweverdescribemultiplephenomena
whichinfluencethelocalizationaccuracy,andformsbasisforfurtherresearchtoimproveonit.
v

C
ONTENTS
LISTOFFIGURES XI
LISTOFTABLES XV
GLOSSARY XVII
1 INTRODUCTION 1
1.1 Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 4DFatigueJIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 AllseasEngineeringB.V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 AcousticEmissionMonitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.1 ApplicationsofAcousticEmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 AcousticEmissionSources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.3 AcousticEmissionWaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.4 AcousticEmissionMonitoringEquipment. . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.5 Acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.6 Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.7 GrowthRateMonitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 ProblemStatement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 ThesisObjective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.6 ThesisOutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 THEORYANDBACKGROUND 11
2.1 WavesinSolidBodies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.1 WaveTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.2 WaveDevelopment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 SignalProcessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3 LocalizationofAESources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.1 LocationUncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3.2 TimePicking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4 LiteratureonSimulationofAcousticEmission . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3 SOFTWAREANDMETHODS 19
3.1 AxisConvention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 FiniteElementMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.1 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.2 ShearLockingandHourglassMode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.3 Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.4 ConvergenceCriteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 SimulationofSignalProcessing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.1 Matlab. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.2 SignalProcessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3.3 SensorResponseSimulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4 SimilarityCriteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4.1 ComparisonMethod. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.4.2 MinimalDegreeofSimilarity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
vii
viii Contents
4 SIMULATIONOFPENCILLEADBREAK 27
4.1 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2 ModelDescription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.1 GeometryandMaterial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.2 SourceModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.3 Discretization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.4 SourceFunctionSelection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3 SimulatedSignals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.1 ComparisonwithExperimentalSignals . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.2 ComparisonwithLambWaveTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.3 Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3.4 TimePicking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.3.5 Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5 SIMULATIONOFFATIGUECRACKGROWTH 41
5.1 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1.1 FatigueTest#1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1.2 FatigueTest#2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2 FiniteElementModeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2.1 MaterialProperties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2.2 ModelofPointandExtendedSource. . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.2.3 ModelofSeparationSource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2.4 Hourglassing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2.5 ConvergenceCheck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.1 PointSource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.2 Extended. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.3 SeparationSource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.3.4 SourceComparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.3.5 WaveTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3.6 PropagationAngle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.4 TimePickingandLocalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4.1 NoiseLevel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4.2 Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.4.3 LocalizationAccuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6 INFLUENCEOFLOCALGEOMETRY 59
6.1 FiniteElementModels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.2.1 Signals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.2.2 EffectofFlange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.2.3 TimePickingandLocalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.3 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7 CONCLUSIONSANDRECOMMENDATIONS 69
7.1 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.1.1 FiniteElementModelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.1.2 AEWaveBehaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.1.3 TimePickingandLocalization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71